1. Field of the Invention
The present invention relates to an image-pickup system equipped with a radiation image-pickup apparatus, a controlling method therefor, and a computer-readable storage medium storing thereon program instructions. The image-pickup system equipped with the radiation image-pickup apparatus may be used for still-image shooting or video shooting such as fluoroscopy.
2. Description of the Related Art
In recent years, image-pickup apparatuses including a flat panel detector (hereinafter abbreviated as an FPD) formed by using a semiconductor material have been commercialized as image-pickup apparatuses that are used to perform a medical image diagnosis or nondestructive testing by using X-rays. The FPD includes two-dimensionally arranged pixels, each of which having a conversion element including a semiconductor material such as a-Si that can convert a radiation into an electric charge and a switching element transferring the electric signal corresponding to the electric charge. The image-pickup apparatus including the FPD is used as a digital image-pickup apparatus performing the still-image shooting such as the general shooting or the video shooting such as the fluoroscopy for performing the medical image diagnosis, for example.
The above-described image-pickup apparatus includes the FPD, a driving circuit driving the switching element, and a reading circuit which outputs the electric signal output from the switching element as image data. A plurality of the switching elements arranged in the row direction are electrically connected to one another via address lines (driving wires) and a plurality of the switching elements arranged in the column direction are electrically connected to one another via data lines (signal wires). The electric signals output from the switching elements are transferred to the reading circuit via the data lines and output from the reading circuit as the image data.
Cross talk is one of the factors responsible for degrading the quality of an image acquired through the image-pickup apparatus. Cross talk occurring in the image-pickup apparatus denotes the influence of an electric signal output from a given pixel, which is exerted on an electric signal output from another pixel. One of the factors responsible for causing cross talk is capacitive coupling occurring between the data line and the electrode of the conversion element in each pixel.
Particularly in radiography, there is radiation that reaches the FPD after passing through a subject or the light corresponding thereto and radiation that reaches the FPD without passing through the subject or light corresponding thereto. An output of a pixel irradiated with the radiation that had reached the FPD without passing through the subject or the light corresponding thereto has a large value. Cross talk occurring during the radiography denotes the influence of the output having the large value, which is exerted on an output of a pixel irradiated with the radiation that had reached the FPD after passing through the subject or the light corresponding thereto. Therefore, the above-described cross talk becomes a significant problem for the image-pickup apparatus used for radiography. For the above-described cross talk, U.S. Pat. No. 5,744,807 discloses a technique for reducing cross talk by connecting a data line to a fixed potential during the radiation-irradiation period and eliminating an induced charge generated by capacitive coupling.
However, the technology disclosed in U.S. Pat. No. 5,744,807 is often inadequate to reduce cross talk. Particularly, U.S. Pat. No. 5,744,807 describes no measures against cross talk occurring in the period from when the connection between the data line and the fixed potential is finished by finishing the radiation irradiation until an operation is started to read the electric charge of a pixel. Particularly when the period is long, the cross talk may be increased based on a time constant determined based on the capacitive or capacitance coupling of the data line and the wiring resistance, and the effect of the technology may become insufficient.
Particularly in an image-pickup apparatus used for radiation imaging (radiography), the accumulation-operation period where each of the switching elements provided in effective pixels becomes non-conductive is determined in advance, and the irradiation of radiation having a dose appropriate for the radiography is performed during a certain period included in the accumulation-operation period. Therefore, the duration between the end of the radiation irradiation and the start of conduction of the first switch element, which is the end of the accumulation-operation period, may be increased depending on the conditions of the radiation irradiation. In that case, the cross talk may be significantly increased.